The present invention relates to a polishing composition used mainly for polishing a silicon carbide wafer, more specifically, for polishing the (0001)Si face of a hexagonal silicon carbide single crystal wafer or the surface of a hexagonal silicon carbide single crystal wafer other than the (0001)Si face such as the (000-1)C face, and to a method for polishing a silicon carbide wafer using the polishing composition.
A hexagonal silicon carbide single crystal wafer such as a 4H—SiC single crystal wafer and a 6H—SiC single crystal wafer is, typically, manufactured through the preliminary polishing step of a wafer surface using slurry containing diamond abrasive grains and the finish polishing step of the wafer surface after preliminary polish. In the finish polishing of a hexagonal silicon carbide single crystal water, a work affected layer of amorphous generated on the wafer surface by preliminary polishing is removed and the wafer surface is flattened after the removal of the work affected layer.
As a polishing composition usable in finish polishing of a hexagonal silicon carbide single crystal wafer, a polishing composition containing colloidal silica with a pH of 4 to 9 has been known as disclosed in Japanese Laid-Open Patent Publication No. 2005-117027. However, the removal rate of polishing a hexagonal silicon carbide single crystal wafer with the polishing composition according to the document is not sufficiently high. Therefore, the time required for finish polishing is extremely long when the polishing composition according to the document is used.
In addition, Japanese Laid-open Patent Publication No. 2001-205555 discloses polishing of a silicon carbide single crystal wafer using a polishing composition containing chromium oxide abrasive grains and hydrogen peroxide. However, chromium oxide contained in the polishing composition according to the document has a possibility of contaminating a wafer by adhering to the wafer surface after polishing in addition to its significant harmful effect on the environment.